Interesting ... I have never seen an enum used like this. Is this just leveraging how it creates a singleton as opposed to having a static initializer such as below?

```java
private static final AlwaysTrue INSTANCE = new AlwaysTrue();
```

or


```java
private static final Func1<T, Boolean> ALWAYS_TRUE = new Func1<T, Boolean>() {
       @Override
       public Boolean call(Object o) {
           return true;
       }
}
```